Tappet assembly



Nov. 22-, 1966 M. v. DADD TAPPET ASSEMBLY Filed Nov. 4, 1964 ATTORNEYS United States Patent Ofifice 3,286,702 Patented Nov. 22, 1966 3,286,702 TAPPET ASSEMBLY Morris V. Dadd, Muskegon, Mich., assignor to Johnson Products, Inc., Muskegon, Mich., a corporation of Michigan Filed Nov. 4, 1964, Ser. No. 408,994 3 Claims. (Cl. 123-90) This invention relates to internal combustion engines having an overhead cam shaft, and particularly relates to the valve train assembly of an overhead cam shaft engine, especially the tappet subassembly.

Modern engine developments enable constantly increasing engine speeds, to allow relatively larger output ratings from relatively smaller engines. Increasing engine speeds require the valve train for each Valve to move at greater frequency and speed of reciprocation. The weight of the valve train thus becomes crucial, since it must be constantly accelerated to its top speed, stopped, and accelerated in the opposite direction, at extremely high frequencies.

One effective method of decreasing valve train weight is to provide an overhead cam shaft to operate the valves directly through the tappets without the necessity of push rods and rocker arm assemblies. Presently, however, overhead cam arrangements are limited to structures having mechanical tappets due to the absence of an effective hydraulic tappet assembly for an overhead cam shaft engine. Mechanical tappets result in noisy operation, and present lash adjustment problems by their very nature.

It is an object of this invention to provide a unique engine valve train assembly achieving hydraulic lash adjustment in an overhead cam engine.

Another object of this invention is to provide an overhead cam engine with hydraulic tappets uniquely held aligned directly between the valve stem and the cam of the overhead cam shaft, and yet retained outside the cylinder head of the engine.

Another object of this invention is to provide an overhead cam shaft engine which hydraulic tappets capable of being removed and reinstalled without disruption of the engine head or block, merely by removal of the cover over the cam shaft and tappets.

A further object of this invention is to provide an inverted mushroom head tappet of hydraulic lash adjusting characteristics capable of direct high speed operation from the cam shaft to the valve through the hydraulic tappet, without rocker arms or push rods. The assembly can moreover he manufactured according to normal engine tolerances.

It is another object of this invention to provide a unique removable mounting bracket assembly for inverted hydraulic tappets held above and outside the cylinder head between an overhead cam shaft and the engine valve extending through the cylinder head.

These and several other objects of this invention will become apparent upon studying the following specificati-on in conjunction with the drawing, in which:

The figure is a fragmentary enlarged, partially sectioned view of an engine assembly, showing the valve train for one valve.

Since each of the individual valves in the engine assembly extends through the cylinder head to the individual cylinders in the same fashion, and since the tappet and holding assembly shown in the figure is exactly the same for each valve, only one is shown to prevent unnecessary duplication in the drawing.

Referring to the drawing, engine assembly includes a conventional internal combustion engine having a plurality of cylinders and pistons therein to drive a crank shaft (not shown) for power output. The engine includes a cylinder head 12 of conventional construction, having intake and exhaust engine valves 14 for each cylinder, and extending through the head so that the tip 16 of the valve stem protrudes from and above the engine cylinder head.

The valve stem rides within the bore provided in the cylinder head and within extended guide bushing 18. It includes a reduced diameter neck 20 around which a diskshaped keeper 22 is fitted to retain compression spring 24 between it and the cylinder head. Mounted in the overhead position above the valves and cylinder head is the overhead cam shaft 26 which includes a plurality of spaced cams 28, one for each valve, and each having a base circle 30 and an operating camming lobe 32 in conventional fashion.

Mounted adjacent each valve and each respective cam is a special tappet bracket 34. Each bracket includes a main stem 32 with a lower axial end abutting the cylinder head. A passage 36 extends through the stem to receive a mounting bolt 38 threadably engaged with the cylinder head. Extending integrally from this stem is a radial arm 40 having an integral annular collar 42 at the outer end thereof. This collar has a through passage extending vertically, in alignment with cam shaft 26 and the respective valve 14 generally parallel to bracket stem 32. Received in this annular collar is an inverted, mushroom head, hydraulic tappet 50.

Tappet 50 includes a tappet body 52 which is generally hollow and cylindrical in configuration. It is inverted, having an open lower end communicating with its hollow interior, and a closed upper end enlarged in diameter to form a mushroom-shaped cam contact surface 56. Around the periphery of the tappet housing is an annular reduced diameter grooved portion 58 communicating with an annular inner diameter groove 60 in collar 42, to form an annular passage. This annular passage communicates with a passgeway 64 extending through radial arm 40 of the bracket, which in turn communicates with passage 36 in the bracket stem; Passage 36 has a diameter slightly larger than stud 38 to allow oil flow from passage 68 in the cylinder head. This passage 68 communicates with a pressurized source of oil (not shown) in the engine in conventional fashion so that oil will flow through passage 68, passage 36, passage 64, passage 60, and thence, through port 70 in the wall of the tappet housing to its hollow interior.

0n the centerline of the tappet housing, inside its hollow interior, is an integral abutment pillar 72. Axiallyabutting this is a lash adjusting plunger 74 which is fitted inside a hollow lash adjuster body 76. This lash adjuster body is cylindrical in configuration, generally hollow, and has a closed lower end which forms a valve abutting surface in operative contact with the valve stem tip 16. An oil passage 78 extends axially through plunger 74, communicating through a port 80 with the hollow interior of the tappet body. A plate-type check valve 84 is against the lower nose of plunger 74 to close off this passageway under pressure in the 'high pressure chamber 88 between plunger 74 and lash adjuster body 76. The valve is retained in place by a return spring 91 in an orificed retainer cup 90. The cup is held by compression spring 92 between it and the enclosed lower end of lash adjuster body 76. A small bleed port 102 extends between the upper end of the pressure chamber and the outer wall of plunger 74. A snap ring 96 received in a groove on the open upper end of the lash adjuster body retains the lash adjuster on the plunger. The three components of the tappet, i.e. the tappet housing, plunger, and lash adjuster body are in sliding engagement. The lash adjuster body is between the other two, but the plunger also abuts column 72 of the housing. Spring 92 in chamber 88 maintains plunger 74 is tight abutment with this column 72.

Optionally, an air bleed port 100 may extend from the hollow reservoir inside the tappet body at its upper end, to the exterior of the tappet body, so that when the tappet is in the elevated position as illustrated in dotted lines, port 100 can vent any air bubbles in the reservoir above collar 42.

In operation, therefore, cam shaft 26 operates directly through the hydraulic tappet on the foot or end of each engine valve stem to reciprocate the valve. Relative movement between plunger 74 and lash adjuster body 75 achieves constant lash adjustment with flow of oil through the several passages and past check valve 84 into the pressure chamber on the return stroke.

In this valve train and engine assembly, the distance advantage normally obtained from the location of the pivot axis of the rocker arm is not present, so that the tappet must move the same distance as the valve rather than a smaller distance. Hence, the lob on each cam of the cam shaft must have greater lift than normal, in fact sufficiently great to achieve this one-to-one movement for complete opening of each valve. Therefore, greater cam velocities are necessary which require larger cam face surface of the tappet. The enlarged, mushroomshaped head at' the upper end of the hydraulic, inverted tappet is important to the most effective operation of this system, to achieve proper cam shaft to tappet cam face cont-act with the increased velocity.

It will be realized that the tappet assembly is completely inverted from that normally presented, due to the unusual arrangement. Also, the tappet is relatively short in length considering its function. All of the hydraulic tappets are mounted completely outside the cylinder head of the engine, to be retained above the cylinder head in this unique fashion.

In fact, removal and replacement of the tappets becomes quite simple without major disruption of the engine. This can be achieved by collapsing the tappet by gripping the upper and lower ends of the tappet and squeezing it together with a pliers-type wrench, to force 'liquid out of the pressure chamber and shorten the overall length of the tappet, then loosening stud 38, and rotating bracket 34 on the stud to remove the tappet out of alignment with its cam and valve for removal. Replacement is just as simplewith sliding insertion of a collapsed tappet into the collar, swiveling of the collar into alignment between the cam and valve, and tightening stud 38. The tappet would be extended to its operative length by spring 92. The valve train load is supported during valve open portion of the. cycle by the oil trapped in the high pressure chamber 88.

Many noted advantages are achieved from the novel inverted, mushroom head, hydraulic tappet valve train assembly in combination with an overhead camshaft. Additional advantages will probably occur to those in the art upon studying the invention. Also, it is conceivable that certain minor details of construction could be changed within the broader concept presented. Hence, this invention is intended to be limited only by the scope of the appended claims and the reasonable equivalents thereto.

I claim:

1. An inverted hydraulic tappet assembly for an overhead cam shaft engine having valves with stems extending 65 up through the cylinder head, an alignment bracket attached to the cylinder head adjacent each valve, and having an alignment collar between the valve and the adjacent cam of the cam shaft; an inverted hydraulic tappet slidable in said collar; said tappet including a hollow tappet housing having an enlarged, upper mushroomed 5 head in operative contact with the respective cam of the cam shaft, and having an open lower end; a hollow lash adjuster body in said open lower end and having a closed lower end projecting into operative contact with the upper end of the valve stem; a plunger inside said hollow lash adjuster body, with its upper end in abutment with said tappet housing; a pressure chamber between the lower end portion of said plunger and the closed end of said lash adjuster body; a passage through said tappet housing and a communicating passage through said plunger to said pressure chamber; a check valve on the lower end of said passage to prevent backward flow from said pressure chamber through said plunger; and oil passage means through said bracket and collar from the cylinder head, to said tappet housing passage and said plunger passage for flow to said pressure chamber.

2. The assembly in claim 1 wherein an air bleed port extends from the upper end of the hollow tappet body interior through said body, above said collar in the raised tappet position.

3. A tappet and bracket assembly for mounting above the cylinder head of an overhead cam engine, comp-rising: a bracket having a stem including attachment means for securing said stem to the top of an engine cylinder head; a radial arm extending from said stern and terminating in an annular collar having a cylindrical tappet-receiving opening extending therethrough; and fluid passage means extending through said stem, arm, and collar into said opening for supplying a tappet therein; an inverted hydraulic tappet slidable in said collar; said tappet including a hollow tappet housing having an enlarged, upper mushroomed head for operative cam contact and having an open lower end; a hollow lash adjuster body in said open lower endand having a closed lower end projecting for operative contact with the upper end of a valve stem; a plunger inside saidhollow lash adjuster body, with its upper end in abutment with said tappet housing; a pressure. chamber between the lower end portion of said plunger and the closed end of said lash adjuster body; a passage through said tappet housing and a communicating passage through said plunger to said pressure chamber; a check valve on the lower end of said passage to prevent backward fiow from said pressure chamber through said plunger; and oil passage means through said bracket and collar from the cylinder head, to said tappet housing passage and said plunger passage for flow to said pressure chamber.

805,109 11/1958 Great Britain. 903,983 8/1962 Great Britain.

MARK NEWMAN, Primary Examiner. AL LAWRENCE SMITH, Examiner. 

1. AN INVERTED HYDRAULIC TAPPET ASSEMBLY FOR AN OVERHEAD CAM SHAFT ENGINE HAVING VALVES WITH STEMS EXTENDING UP THROUGH THE CYLINDER HEAD, AN ALIGNMENT BRACKET ATTACHED TO THE CYLINDRE HEAD ADJACENT EACH VALVE, AND HAVING AN ALIGNMENT COLLAR BETWEEN THE VALVE AND THE ADJACENT CAM OF THE CAM SHAFT; AN INVERTED HYDRAULIC TAPPET SLIDABLE IN SAID COLLAR; SAID TAPPED INCLUDING A HOLLOW TAPPET HOUSING HAVING AN ENLARGED, UPPER MUSHROOMED HEAD IN OPERATIVE CONTACT WITH THE RESPECTIVE CAM OF THE CAM SHAFT, AND HAVING AN OPEN LOWER END; A HOLLOW LASH ADJUSTER BODY SAID OPEN LOWER END AND HAVING A CLOSED LOWER END PROJECTING INTO OPERATIVE CONTACT WITH THE UPPER END OF THE VALVE STEM; A PLUNGER INSIDE SAID HOLLOW LASH ADJUSTER BODY, WITH ITS UPPER END IN ABUTMENT WITH SAID TAPPET HOUSING; A PRESSURE CHAMBER BETWEEN THE LOWER END PORION OF SAID PLUNGER AND THE CLOSED END OF SAID LASH ADJUSTER BODY; A PASSAGE THROUGH SAID TAPPER HOUSING AND A COMMUNICATING PASSAGE THROUGH SAID PLUNGER TO SAID PASSAGE CHAMBER; A CHECK VALVE ON THE LOWER END OF SAID PASSAGE TO PREVENT BACKWARD FLOW FROM SAID PRESSURE CHAMBER THROUGH SAID PLUNGER; AND OIL PASSAGE MEANS THROUGH SAID BRACKET AND COLLAR FROM THE CYLINDER HEAD, TO SAID TAPPED HOUSING PASSAGE AND SAID PLUNGER PASSAGE FOR FLOW TO SAID PRESSURE CHAMBER. 